Clean up some old scripts in libphutil

Summary:

• envinfo.php has been obsoleted by:
  • __init_script__.php just sets all this stuff to the right value now.
  • support/debug.php provides a more general mechanism to get arbitrary environmental data from users.
• kill_init.php facilitated the removal of __init__.php files, but we did that a long time ago and I haven't seen any users run into issues in many months.

Test Plan: N/A

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D6377